The present invention relates to a method of producing tubular wrappings preferably, but not necessarily, of parallelepiped shape or similar.
In particular, the present invention relates to a method which may be used to advantage on cigarette packing machines, for producing the tubular outer wrapping or transparent tubular wrapping of so-called soft packs.
On known packing machines, tubular wrappings of the aforementioned type are normally produced by successively feeding sheets of wrapping material over respective peripheral openings formed about a wrapping wheel and each defining the access to a respective radial seat on the same. The wheel is jogged about its axis so as to successively feed said seats to a loading station where each seat is arrested long enough to receive the product for wrapping. Insertion of the product inside the seat is usually accompanied by simultaneous insertion of the sheet of wrapping material over the opening, which is gradually folded in a U about the product as this enters the seat. The sheet of wrapping material is usually of such a length that, when the product is fully inserted inside the seat, the opposite end portions of the sheet project outwards of the same.
The loading station usually presents a first folding device which, subsequent to insertion of the product and prior to rotation of the wrapping wheel, is activated for folding down on to the product a first of said end portions, usually the one located upstream in relation to the traveling direction of the seat. The wheel is then jogged forward one step to bring the next seat into the loading station and feed the previous seat beneath a fixed outer plate designed to engage the second of said end portions and fold it back on to the product so that it at least partially overlaps the first portion. For one or more successive steps of the wrapping wheel, the product, with the end portions of the sheet folded as described above, slides beneath the fixed outer plate, which provides for holding down the folded end portions one on top of the other.
The above situation continues until the product is arrested by the wrapping wheel at a joining station, at which point the fixed plate terminates and the product is arrested in such a position as to project partially from the end of the plate, but with a sufficient portion still engaged by the same for holding the end portions of the sheet folded down one on top of the other. At this point, an external joining device, e.g. a gumming or welding device at the station, acts on the part of the two end portions projecting from the fixed plate, so as to join the end portions together and so form the tubular wrapping.
The above known method therefore requires the use of a jog feed device, n this case, a jog type wrapping wheel, for at least enabling operation of the joining device.